1. Field of the Invention
The present invention relates a communication apparatus, communication method, and communication system which perform media access control and, more particularly, to access control for improving quality of service (QoS).
2. Description of the Related Art
Media access control (MAC) is control for causing a plurality of communication apparatuses which perform communication while sharing the same medium to decide how to use the medium in transmitting communication data or management frame. Owing to media access control, even if two or more communication apparatuses transmit communication data (or management frame) by using the same medium at the same time, there is less chance of the occurrence of a phenomenon (collision) in which a communication apparatus on the receiving side cannot decode communication data. The fundamental access method of the IEEE802.11 MAC is CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). The CSMA/CA is designed to reduce the collision probability. Media access control is also a technique for controlling access from communication apparatuses to a medium so as to minimize the chance of the occurrence of a phenomenon in which, despite the presence of communication apparatuses having transmission requests, the medium is not used by any of the communication apparatuses.
In addition, several access control techniques designed to improve quality of service (QoS) are also known. For example, there is available HCCA (HCF Controlled Access) which is an extended technique of a conventional polling sequence and is used as a QoS technique of guaranteeing parameters such as a designated bandwidth and delay time. According to HCCA, in order to guarantee parameters such as bandwidth and delay time, QAP (QoS Access Point) performs bandwidth management including allocation of transmission opportunity to QSTA (QoS Station). QAP is also known as HC (Hybrid Coordinator) in IEEE802.11e standard.
Jpn. Pat. Appln. KOKAI Publication No. 2002-314546 discloses a method of assigning priorities to communications between wireless network stations, while referring to QoS in the IEEE 802.11e standard.
According to conventional HCCA, quality can be guaranteed for each traffic stream, and data transmission corresponding to priority can be realized. A Traffic Stream is a set of MSDU (MAC Service Data Unit) s to be delivered subject to the QoS parameter values provided to the MAC in a particular traffic specification. Traffic Streams are only meaningful to MAC entities that support QoS within the MAC data service. Such QoS is also preferably used in a new communication scheme in which a further increase in throughput is achieved. For example, QoS is preferably used for frame aggregation designed to improve the transmission efficiency by transmitting a plurality of MAC frames upon containing them in one PHY (physical) frame. If, however, a conventional frame aggregation technique is simply applied to QoS like HCCA, the following problems arise.
According to the conventional frame aggregation technique, since no consideration is given to the priorities of frames, when a series of frames in a transmission queue (TxQ) are aggregation target frames, an FTP (File Transfer Protocol) frame with a relatively low priority may be extracted before a VoIP (Voice over IP) frame with a high priority and aggregated to a transmission aggregation frame. This may hinder the assurance of QoS in consideration of the priorities of frames.
In addition, the frame aggregation technique using a selective repeat retransmission needs to be in combination with an acknowledgement sequence (e.g., a “No acknowledgement”) unique to IEEE802.11e standard.